JPS6337070B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a ZrB ₂ (zirconium diboride) sintered body. In general, metal boride ceramics have the characteristics of high melting point, high hardness, high strength, and high corrosion resistance, and have traditionally been used as cutting tools and heat engine parts materials, but although they have not been put into practical use yet. Most of them are titanium borides, and the reality is that zirconium borides are hardly ever put into practical use. The _ZrB2 composite sintered body of the present invention has a high melting point, high strength,
It has excellent characteristics such as high corrosion resistance, high hardness, electrical conductivity, and oxidation resistance, so it is a material that can be widely used for high-temperature corrosion-resistant parts, mechanical parts, heating elements, electrodes, crucibles for induction furnaces, etc. (Prior Art) There are currently very few ZrB _2- quality composite sintered bodies that are in widespread practical use, but various ones have been proposed in patents and the like. That is, silicides such _{as MoSi 2 ,}
Nitrides such as TaN, H _f N, and BN, oxides such as ZrO ₂ , carbides such as SiC and B ₄ C, and various metals are known. (Problems to be solved by the invention) For example, regarding silicides, the Japanese Patent Publication No. 38-6098
ZrSi ₂ and MoSi ₂ are disclosed in U.S. Patent No. 3705112, but these Si-based compounds melt or decompose during sintering in a high-temperature atmosphere, resulting in porous structures and slow crystal grain growth. Often larger,
Therefore, the strength and corrosion resistance are often insufficient, and although the oxidation resistance is expected to be effective as a SiO ₂ film, these subcomponents alone are not sufficient for use in air. Next, regarding nitrides, U.S. Patent No. 3305374
TaN disclosed in ZrB ₂ as a high hardness material,
Added to TiB ₂ , etc., and applied to tool materials and decorative materials, it is excellent in terms of high hardness and high strength, but is used in high-temperature oxidizing atmospheres such as high-temperature corrosion-resistant parts, heating elements, electrodes, induction furnace crucibles, etc. In this case, the oxidation resistance, spalling resistance, corrosion resistance, etc. are not sufficient. Next, regarding carbides, refer to U.S. Patent No. 3775137.
SiC, B ₄ C and SiC are disclosed in U.S. Patent No. 3,325,300, but the addition of only SiC as in U.S. Pat. No. 3,775,137 is insufficient in terms of oxidation resistance, and
When MoSi ₂ + B ₄ C and MoSi ₂ + SiC + B ₄ C are added to 3325300, MoSi ₂ has a lower melting point than the sintering temperature and melts during sintering, decomposing and promoting grain growth, making the structure porous. Therefore, it is difficult to increase the density. Therefore, it has not yet reached the level of a material that is particularly required as a high-temperature structural member. In view of these points, the present inventors added SiC+B ₄ C without adding MoSi ₂ first, or added SiC+BN without adding MoSi 2 first.
We have studied and improved products with the addition of
We succeeded in obtaining a ZrB ₂ sintered body. Although these methods made it possible to put ZrB ₂ sintered bodies to practical use, it was also true that there was still room for improvement. For example, the addition system of SiC + BN was satisfactory in that spalling resistance could be improved by increasing the BN content, but the addition of BN, which is difficult to sinter, resulted in a dense sintered body. It is difficult to obtain such a material, and its strength and hardness are not necessarily sufficient, so it cannot be said to be suitable for applications such as high-temperature, high-strength members. In addition, although the SiC + B ₄ C additive system was satisfactory in terms of strength, hardness, and oxidation resistance, it was not necessarily sufficient in terms of spalling resistance and corrosion resistance, and therefore it was not suitable for use in steel, etc. It could not be said to be suitable for uses such as spalls and corrosion-resistant members. In view of these points, we are conducting research to overcome the conventional problems with the ZrB ₂ -material sintered body, which has excellent properties but is not fully utilized and is actually used for only extremely limited applications. As a result of this progress, we have achieved a combination of various properties such as excellent high density, high strength, oxidation resistance, corrosion resistance, and even spalling resistance, and in some cases, we have significantly improved the strength of this type of composite. They succeeded in developing a sintered body. (Means for solving the problem) That is, the present invention has ZrB ₂ as a main component, 1 to 15% SiC, 5 to 20% B ₄ C, and 3 to 25% by weight.
This article focuses on a high-strength ZrB _dual- composite sintered body characterized by the inclusion of BN. The ZrB ₂ used in the present invention can be obtained, for example, by reacting a mixture of zirconium oxide, boron oxide, and carbon at high temperatures, and it is preferable to use ZrB 2 with the highest possible purity for producing the present sintered body.
Further, a powder having a particle size as small as possible is preferable. Specifically, it has a purity of 99% or more and an average particle size of 10 μm or less, especially 1 μm or less. In addition, SiC, B ₄ C and
Regarding BN, it is sufficient that it is present in a predetermined amount as such a compound in the form of a sintered body, so it may be blended in any form as a starting material, but other than SiC, B ₄ C and BN may be used. When using these raw materials, special consideration is required in the sintering stage, so it is best to prepare SiC, B ₄ C, and BN as the usual blended raw materials. The raw materials for SiC, B ₄ C and BN are preferably as high in purity as possible, usually at least 99%. The raw material mixture is usually prepared by uniformly mixing these three types of fine powders, but the same effect can be obtained by ultrafinely pulverizing them for the purpose of pulverizing and mixing. In general, the particle size of the mixed raw material is preferably 10 μm or less, preferably an average particle size of 1 μm.
It is necessary to make sufficient adjustments to below m. It is appropriate to use SiC balls for these pulverizations. The sintered body of the present invention can be obtained by filling a graphite mold with these mixtures and hot-pressing the mixture in vacuum or in a neutral or reducing atmosphere such as argon, helium, or carbon monoxide, or by rubber-press molding the mixture. It can be obtained by, for example, baking under normal pressure. Note that the firing temperature is 1800 to 2300°C, and the firing time is usually about 0.5 to 5 hours, although it depends on the size of the sample. In the sintered body of the present invention, SiC (silicon carbide) is required to be at least 1% by weight (the same applies hereinafter), because if it is less than that, the oxidation resistance will not be sufficient and it will be difficult to achieve high density. On the other hand, if it is too large, the effects of spalling resistance and high corrosion resistance will not be exhibited, so it is undesirable and needs to be kept at a maximum of 15%, and is preferably 3 to 10%. At least 5% of B ₄ C (boron carbide) is required, but if it is less than that, it will be difficult to increase the density.On the other hand, if it is too much, the heat resistance will decrease, which is undesirable. It is necessary to limit it to 20%, preferably 7 to 15%.
At least 3% of BN (boron nitride) is required, but if it is less than this, the characteristics of spall resistance and high corrosion resistance will not be fully exhibited, while if it is too much, sintering becomes difficult and high density products are required. This is not preferable because it cannot be obtained, so it is necessary to limit it to a maximum of 25%, and preferably 5 to 20%. In addition, the total amount of SiC, B ₄ C, and BN is required to be at least 9%, and it is possible to have a maximum of 60%, but if the total amount is too large, the characteristics of ZrB ₂ will be impaired. Usually, a total amount of 15 to 50% is appropriate. The sintered body of the present invention consists of components other than these subcomponents, i.e., the remainder, which essentially consists of ZrB ₂ , but components other than ZrB 2 , such as TiB ₂ , may be added to the extent that the characteristics of the ZrB ₂ quality are not impaired _. Of course, there is no problem even if a small amount of is contained, but it is desirable to keep the amount as small as possible. In addition, other components may of course be included as subcomponents as long as they do not essentially impair the intended effects of the sintered body of the present invention, but they must be kept in as small a quantity as possible, including unavoidable impurities. It is. The structure of the sintered body of the present invention is that ZrB ₂ microcrystals consisting of particles with an average grain size of several μm are uniformly dispersed, and subcomponents exist around and between the ZrB ₂ crystal grains.
It had a dense microstructure in which BN, B ₄ C, and SiC were distributed. In addition, in tissues containing 15% or more of BN, BN
Because it has lubricity, BN itself has a diameter of several μm,
It consisted of a plate-like structure with a length of about 8 μm, and existed around fine crystal grains of ZrB ₂ , which was the main component. The other subcomponents (B ₄ C, SiC) were uniformly dispersed between the ZrB ₂ crystal grains as almost granular microcrystals. (Effects of the Invention) The thus obtained sintered body of the present invention has high density, high hardness, particularly high strength, and is a conductive sintered body with excellent corrosion resistance and spalling resistance, so it can be heated at high temperatures. It can be preferably applied to structural members, high-temperature corrosion-resistant members, heating elements, etc., and can also be used in various other applications that exhibit the characteristics of ZrB _binary sintered bodies, so it has great practical value. (Example 1) Γ Example 1 ZrB ₂ powder (purity 99% or more) B ₄ C powder (purity 99%)
% or more), BN powder (purity of 99% or more), and SiC powder (purity of 99% or more) were pulverized and mixed for 3 days using a pot mill using SiC balls in an ethanol solvent in order to thoroughly mix and pulverize them. The obtained powder was thoroughly dried by removing alcohol with an evaporator to obtain a powder with an average particle size of 0.15μ. This powder was molded using a rubber press at 2000Kg/cm ² under an argon atmosphere.
It was fired at 2300°C for 2 hours under normal pressure. Table 1 shows the properties of the sintered body thus obtained. Γ Example 3 The same ZrB ₂ powder, SiC powder, B ₄ C powder, and BN powder as in Example 1 were mixed and ground in a pot mill for 3 days using SiC balls in an ethanol solvent. This powder was thoroughly removed with alcohol using an evaporator and dried to obtain a powder with an average particle size of 0.15 μm.
Fill a graphite mold with this powder and
It was heated at 2050° C. for 30 minutes while pressurizing to Kg/cm ² . Table 1 shows the properties of the sintered body thus obtained. Γ Examples 2 and 4 to 6 and Comparative Examples 7 to
12 Table 1 shows the results for each sample obtained by adjusting the predetermined mixed raw materials according to Examples 1 and 3 and processing them under the predetermined firing conditions. Note 1 Oxidation resistance is the rate of weight increase (unit area (cm ² )) under oxidizing atmosphere at 1000℃ x 12 hours
It is expressed in per dose increase (mg). ) Note 2: Thermal shock resistance is the flexural strength of a sample that was rapidly heated to each temperature for 2 minutes in an electric furnace and rapidly cooled in water, and is the processing temperature at which the strength suddenly decreased, and is expressed as ΔT.

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Claims (1)

[Claims] 1 ZrB ₂ as the main component, 1 to 15% by weight
A ZrB _binary composite sintered body characterized by containing SiC, 5 to 20% B ₄ C, and 3 to 25% BN. 2. The sintered body according to claim 1, wherein the total amount of SiC, _B4C , and BN is 15 to 50%.